The invention relates to a method for replacing digital load cells in a weighing system.
A weighing system often comprises a load-receiving device, which serves for supporting objects intended for weighing. Such a load-receiving device has a number of associated load cells. There are generally 4 load cells, since a load cell is fitted in each corner of the usually rectangular load-receiving device. If these cells are digital load cells, they are normalized, linearized and temperature-compensated even before installation, that is during production, in an automatic process. After undergoing this process, the digital load cells provide a counter reading from 0 to 240000 n digits, for example, over the intended weighing range. If installed in a weighing system with a load-receiving device, the digital load cells are connected to one another via a measuring bus. The measuring bus is also connected to a control unit, for example a terminal, which controls and monitors the digital load cells or the weighing system.
The terminal may comprise evaluation electronics or a data-processing device (PC). When it is first used, the weighing system must then first be connected to the terminal and calibrated. For this purpose, a so-called basic adjustment is carried out to establish the nominal load of the weighing apparatus for the load-receiving device. In this adjustment, a “gross counter reading” (sum of the counter readings of the individual digital load cells) is determined and normalized to a counter reading of, for example, 120000 n digits for the weighing apparatus. During the adjustment, in the sequence in which the corners are subjected to loading the digital load cell is assigned to the respective corner on the basis of the bus address, to permit unique identification of the digital load cell in the later possible event of a replacement being necessary.
After the replacement of a defective digital load cell, it has until now been necessary for the complete basic adjustment, that is calibration, to be carried out once again.
DE 100 41 251 A1 discloses a calibratable weighing system with a data-processing device in which at least one digital load cell serves for storing the load cell parameters and additional system parameters. In each weighing process, these parameters are coded and sent with the weight data to the data-processing device, where they are compared with the parameters likewise stored. If a discrepancy is established in this comparison process, the weighing process is discontinued or at least an error message is displayed. In this case, the data-processing device can be replaced without the weighing system having to be newly calibrated. It is also possible to replace a complete load-receiving device with all the load cells on the data-processing device without the weighing system having to be newly calibrated, since the load-receiving device can in principle be calibrated as a unit and all the parameters of the calibration are stored in the memories of the digital load cell. The parameters can then be read back by the data-processing device after the replacement of the load-receiving device. However, this document does not contain any proposal allowing only individual cells of the digital load cells of the load-receiving device to be replaced.
However, in the case of large weighing systems and/or weighing systems that are installed in the ground with load-receiving devices, it is not always possible to replace the load-receiving device in its entirety. Replacing one or more digital load cells of a load-receiving device has until now always meant that a new calibration process has to be performed.
A similar situation applies to weighing systems which substantially comprise a load cell system and manage without an actual load-receiving device, for example weighing systems for silos in which a load cell is fitted in each supporting leg of the silo.